There is known an electret filter formed from filmsplit fibers, or fibers obtained by splitting a film, as disclosed in Japanese Patent Publication No. 56-47299. This publication mentions the fibrillation of a film into small fibers, but does not contain any description as to the shape, or other specific details of the fibers. Moreover, it does not contain any statement concerning the meshes of any network fleece formed by film-split fibers, or the performance of any filter formed from such fleeces. The examples which it describes cannot necessarily be considered to show any electret filter having a high collecting efficiency with a small pressure loss.